electrostatic charges in a water storage tower tank

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VINSA01

Member
We have a case of electrostatic charges in a water storage tank tower

The tower is around 45 m height and it?s being reported by several workers that during some maintenance maneuvers at the top of the tower They have suffer some electric arching

The tower has no grounding

The tower have six anchoring bolted reinforced concrete bases

We believe that due to the wind the whole structure is positive charged and that the anchoring to the concrete bases are not enought to drain in time the electrostatic charges

Our solution will be to : build a 2/0 Cooper wire grounding ring around the structure in a trench of at least 0.6 m deep
along with one copperweld rod per leg. All the joints will be link using cadweld and grafite.

Each leg will be connected first to the Cooper weld rod and later to the ring

We hope to solve two problems

1.- To drain the static electricity
2.- To drain electricity in case of a lightning strike ( The water tank has at least 3/16 " thickness)

I?ll appreciate your comments
 
C

Cold Fusion

Senior Member
Location
way north
VINSA01 said:
...electrostatic charges in a water storage tank tower

...The tower has no grounding

...The tower have six anchoring bolted reinforced concrete bases

1.- To drain the static electricity
2.- To drain electricity in case of a lightning strike ( The water tank has at least 3/16 " thickness)
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Vin - a couple of questions:

This is a steel tank, steel structure to the concrete bases, concrete bases are in direct contact with the earth?

If so, the tank appears pretty well grounded to me. Concrete and steel in direct earth contact generally has a pretty low resistance to ground. I'd recommend getting a copy of NFPA 780. The resistance to earth for lightning protection or a drain for static buildup is pretty high.

What is the crew touching when they get shocked? They have climbed the ladder, are sitting on the tank, in contact with the tank, all the steel on the tank should be bonded together. What is shocking them? Is it when they touch tools that are plugged into an extension cord brought up from the ground? Is it when they touch light fixtures such as hazard warning lights?

I recommend doing a fall-of-potential ground resistance test to see what the value is before changing. See how that value matches up with that recommended in NFPA 780.

If you end up putting in a ground ring, The rods are near useless. Rather, I'd recommend:
1. Increase the burial depth to .75 meters.
2. Dig the ground ring ditch with a narrow bucket, and pour 15cm of concrete over the ground ring wire.

That will work far better than any ground rods.

I'd also do an after FOP check on the ground resistance. I suspect it won't change much

Your best guides are NFPA 780 and IEEE 142 (green book)

Let us know how it comes out. I'll particularly be interested in the before and after FOP ground resistances.

cf
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Well additional grounding certainly will help at dissipating any lighting strikes. Beyond that, you have not included enough information to make any determination on reducing the arcing experienced by maintenance personnel. Perhaps the maintenace equipment or personnel are the subject of the electrostaticy charge and the arcing occurs because the tank is grounded. Could be the arcing is a result of the tank being adequately grounded and it is dissipating fault current from defective maintenance equipment.

I assume the tank is on one side of the arc... what object is at the other side of the arc? Is there any means by which the object could have been energized by an electrical system? How much water is in the tank? Is the water piping conductive? If so is it bonded in any way to earth, even by being routed underground? Is there any electrical equipment installed on the structure?
 
Smart $

Smart $

Esteemed Member
Location
Ohio
KWH said:
Doesn,t concrete actually act more like an insulator.
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Depends on the moisture content. I don't have any specific numbers but I understand that moist concrete resistivity is on the order of a semiconductor, while dry concrete is on the order of a reasonably good insulator.
 
cadpoint

cadpoint

Senior Member
Location
Durham, NC
...
All the joints will be link using cadweld and grafite.
...
Click to expand...

What does grafite have to do with the cadweld ?

Is this a prep or some certain way you use grafite before the shoot?

Teach me something! :D
 
ELA

ELA

Senior Member
Occupation
Electrical Test Engineer
Have you attempted to measure the voltage on the tank to ground? (with care of course)
If it is electrostatic in nature then your normal volt meter may be enough to discharge it.

If it shows a large voltage with a normal DVM then it may not be static. You can test by using various resistors in parallel with your meter to determine the source impedance.

You can rent or buy an electrostatic voltmeter and measure whether or not the tank has a significant electrostatic charge.

It does not take a vary low impedance ground to dissipate an electrostatic charge in most cases.
 
V

VINSA01

Member
to answer some of your questions

to answer some of your questions

The bases or foundation of the tank are made of reinforce concret at least 2 m deep and in a ring joining the six legs . I expect to have the foundation drawing soon.

The workers refer to feel induction electricity when the aproach a scrub driver close to the 500 m3 water tank they could see the electricity arching.

The FOP test I suppose I have to do it at the foot of the tower

In one of the API Recomended practic says about Static electricity that even 1 Mega Ohm resistance is able to drain these charges . So I trent to belive the Static Charges are not generated by effect of wind.

To answer to other colleages :

There are 3 pumps 50 HP each in a sump near the tank

The piping is conducting

I found severe NEC (or equivalent) violations as far as grounding

I recommend firt to fix the electrical installation and see if the problems of static charges persist or continues

To improve also grounding of the steel tower to cope with lightning ( following NFPA 780 or simmilar)

The gafite has nothing to do with cadweld . We just put it as a gel around bare cupper buried cables to protect them or to enheance a little bit the contact with the soil around
 
cadpoint

cadpoint

Senior Member
Location
Durham, NC
You need the spec's and the drawing or to chip off a chunk of concrete to be tested, to figure out what others have implied.

This is one of those jobs that that has to many variables to quailfy your side of what you might apply as to what you know is the problem, JMO

Ok, fine fix all the existing "situations" as to what you've found, fine and the question still remains what and how where they experiencing stray voltage?
 
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sgunsel

Senior Member
I seriously doubt that this is an electrostatic charge problem. In reality, even 100 megohms looks like a direct short to static electricity and the resistance through the metal tower legs and concrete bases are likely far less than that (look up Ufer). I agree that you need to better investigate what people are doing on the tower to identify and correct the real poroblem, if there is one, before someone gets hurt. I'd document my findings too.
 
D

dbuckley

Senior Member
Location
Canterbury, New Zealand
sgunsel said:
I seriously doubt that this is an electrostatic charge problem.
Click to expand...
I agree.

I think the OP needs to get a voltmeter out and find out what the true story is here. I think the poster who asked about power tools and extension cables is in the right ballpark, and this could well be a ground to ground problem.

If things are "arcing" then I'd be pretty worried.
 
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ELA

ELA

Senior Member
Occupation
Electrical Test Engineer
Can you tell us more about the construction of the storage tank?
You have said it is a steel tank and you suspected wind generated static electricity?

Is the tank lined with plastic by any chance?

It takes two insulators to generate static electricity.
 
C

Cold Fusion

Senior Member
Location
way north
Smart $ said:
Depends on the moisture content. I don't have any specific numbers but I understand that moist concrete resistivity is on the order of a semiconductor, while dry concrete is on the order of a reasonably good insulator.
Click to expand...
From the point of view of grounding resistances, buried concrete makes an excellect low resistance contact to earth. That is why concrete encased electrodes work as good as they do.

cf
 
C

Cold Fusion

Senior Member
Location
way north
VINSA01 said:
The bases or foundation of the tank are made of reinforce concret at least 2 m deep and in a ring joining the six legs . I expect to have the foundation drawing soon.
Hopefully the steel cage in the foundation is tied to the bolts attaching to the legs. If so, this is the best ground you're going to get. Look at Soares Grounding on Ufer grounds. I did not mention Soares earluer, but it is also an excellent reference.

The FOP test I suppose I have to do it at the foot of the tower
Yes. That will tell you what the resistance to ground is now.

In one of the API Recomended practic says about Static electricity that even 1 Mega Ohm resistance is able to drain these charges . So I trent to belive the Static Charges are not generated by effect of wind.
I suspect you are correct

I found severe NEC (or equivalent) violations as far as grounding

I recommend firt to fix the electrical installation and see if the problems of static charges persist or continues
Yes

To improve also grounding of the steel tower to cope with lightning ( following NFPA 780 or simmilar)
Yes
Click to expand...
..........

cf
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Cold Fusion said:
From the point of view of grounding resistances, buried concrete makes an excellect low resistance contact to earth. That is why concrete encased electrodes work as good as they do.

cf
Click to expand...
Well there are two things that make CEE's "good" for earth grounding: 1) the surface area is greater than that of other rod, pipe, plate electrodes 2) the concrete absorbs the moisture of the surrounding earth. If the moisture content in the surrounding earth is essentially non-existent, the CEE's performance diminishes greatly.
 
tom baker

tom baker

First Chief Moderator
Staff member
Location
Bremerton, Washington
KWH said:
Doesn,t concrete actually act more like an insulator.
Click to expand...

No concrete is considered conductive and thats why it can be used as part of a CEE.
Concrete absorbs moisture and holds it, plus it has a lot of ions, all making it conductive.
HG Ufer tested his original concrete foundations done in WWII after 20 years and they still had low resistance in Arizonia
 
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